Fluid processing apparatuses of this generic type are known in the prior art and are used in various designs, for example, as actuators such as hydraulic working cylinders, as hydraulic accumulators, for example, in the form of piston accumulators, and as a spring-damper element for hydraulic suspension systems or the like. In the case of fluid systems for steering and control processes, measured variables that indicate the state of the fluid are the most important parameters. The determination of measured variables, which is performed in a decentralized manner in the prior art, is disadvantageous for a number of reasons. Thus, for example, a pressure measurement taken via pressure lines is imprecise and prone to errors. In particular in the event that a plurality of state variables must be determined, a great deal of mechanical effort and cabling work is associated therewith.